Psoriasis is common skin disease which is caused by speed-up replacement of human skin cell. In normal condition, skin cells shed and replace themselves in 21-28 days. But in psoriasis, this process can occur in 2-6 days. Psoriasis can affect any ages, any gender and regardless the race. Around 125 million of people around the worlds are affected, or 2-3% of population is living with psoriasis.
Psoriasis is non-contagious from person to person or between the patient's body part itself. Up to now, there is no solid inference that psoriasis can run in families. Several cases show that children whose parent is psoriasis patient also have psoriasis. But some cases reveal the opposite.
About 80% of psoriasis case is plaque psoriasis. This type sometimes is also named with psoriasis vulgaris as it means common. Plaque psoriasis appears with white scales in the top of red and thick patches. The white scales are the skin shedding as the effect of speed-up skin growth. The old scales can be shed by scratching. While the redness patches is due to the increase of blood vessels to support the increase of cell production.
Recent research has found that the change in skin growth is affected by the change in immune system. Certain immune cell (T cell) becomes triggered and overactive. T cell will act as if they were fighting virus, infection or healing the wound. This condition speed-up the skin growth at some body part hence thick plaque is formed. Psoriasis usually occurs in knee, elbow, and scalps, but it can also happen in any part of human body.
To cure psoriasis, physicians have 4 types of treatments. The drug used depends on the psoriasis severity level. For mild to moderate psoriasis, physicians give topical therapies. It is available in creams, lotions, ointments, mousses, and gels. The topical therapies are applied in localized psoriasis. The second treatment is phototherapy. This therapy uses ultraviolet light A (UVA) and B (UVB). Physicians will ask patient to have phototherapy session for several weeks. The third treatment is systemic medication which uses tablets or pills. This treatment have potential side effect to the patient body, hence only patient with moderate to severe psoriasis will undergo this treatment. The fourth or the latest treatment found is biological injection. This treatment only applied to patients with severe psoriasis which other types of treatment can not handle it. The injection will block certain immune cell (T cell) to act, as this speed-up growth is the cause of psoriasis.
Physicians use their knowledge and experience to decide which treatment to be applied. Patient's physical condition which differs from one another also gives extra thought to the physicians to decide it. This includes combination of several treatments, changing dosage and treatment change. In every visit, physicians assess the patient's psoriasis severity as well as monitor the treatment efficacy.
The gold standard to assess psoriasis condition is Psoriasis Area and Severity Index (PASI). In PASI, the human body is divided into four regions: head, trunk, upper extremities and lower extremities. There are 4 parameters that will be determined in every body regions which are psoriasis area, erythema (redness), thickness and scaliness. Each body regions is weighted differently regarding the proportion of body surface area (BSA). Head is weighted 0.1, trunk is 0.3, upper extremities is 0.2 and 0.4 for lower extremities. PASI scoring is calculated using equation below.PASI=0.1(Rh+Th+Sh)Ah+0.2(Ru+Tu+Su)Au+0.3(Rt+Tt+St)At+0.4(Rt+Tt+St)At 
A=area (0-6), R=redness (0-4), T=thickness (0-4), S=scaliness (0-4).
h=head, u=upper extremities, t=trunk, l=lower extremities.
The total PASI score ranges from 0 to 72; higher score indicate more severe psoriasis condition. The treatment is considered effective if the PASI score is reduced by 75% from the initial score.
Although PASI is gold standard to assess the treatment efficacy, this method is rarely used in daily practice. Dermatologist has to assess all lesions and score them for each four parameters: area percentage, erythema, thickness and scaliness. Hence it is a tedious task to do.
To score the thickness of psoriasis lesion, dermatologist slides their index finger on it. They choose a representative lesion among every lesion in each body part; head, trunk, upper extremities and lower extremities. The tactile information from dermatologist's finger is then combined by their knowledge and experience to determine the score. Some dermatologists also access the average thickness PASI score by choosing the most common thickness from all the lesions in that area. This manual and subjective assessment may lead to inter-rater and intra-rater score variation, inaccuracy and inconsistency. Inter-rater variation is the different scores given by two dermatologists, while intra-rater variation is the different scores given by same dermatologist. To have such qualitative assessment, even one dermatologist is possible to give different score in one lesion if asked to conduct second assessment. Thus, objective and quantitative evaluation of psoriasis lesion thickness for PASI scoring is important in deciding the treatment efficacy.
Another method to assess and rate the severity of the psoriasis thickness is by performing biopsy, whereby the said psoriasis lesions are cut and analyzed physically. This is not recommended because it involves physical removal of the said psoriasis lesion even before knowing the severity of the said legion. If the severity is low enough that oral or ointment medication can cure said psoriasis lesion, then the initial step of cutting said lesion is really unnecessary.
The X-ray radiation has also been used to measure the psoriasis thickness. The radiation transmits through the patient's skin and creates a projection image. Due to the usage of X-ray, which has the possibility of exposing hazard radiation to patients, this method is not recommended for daily practice. Furthermore, the X-ray technology needs a skilled person to perform the acquisition.
Another technology used to assess psoriasis lesion thickness is ultrasound. The ultrasound frequency that is commonly used to perform the image acquisition is 15 MHz. Using ultrasound technology as an assessment tool also needs a skilled person to interpret the image and differentiate the skin layers.
It is therefore advantageous if the assessment of the psoriasis lesion thickness for PASI scoring could be objectively and accurately evaluated. This is important in deciding the treatment efficacy, especially in clinical trials. It is also advantageous if the assessment could be used in daily practice and performed by regular physicians.
The present invention overcomes the above shortcomings by providing a method and apparatus for assessing data from digital images of psoriasis lesion for said psoriasis lesion thickness by utilizing a developed computer vision system to obtain Psoriasis Area and Severity Index (PASI) parameters in particular.